This is more a Ruby than a Rails question -- feel free to redirect me
as appropriate -- but either this is a Ruby 1.9 bug or I have some
serious misunderstanding. Essentially, I''ve caught the <=>
operator
returning nil -- not -1, 0, or 1, but nil. Schematically:
class A
attr_accessor :slot
fun matches?(s)
p "s <=> @slot = #{s <=> @slot}"
return (s <=> @slot) == 0
end
end
Driven from a script, I get something like this:
# Case 1: Notice that <=> evaluates to nil when it should eval to 0
a.slot = "dog"
a.matches?("dog")
"s <=> @slot = "
=> false
# Case 2: When I pass a String.new("dog") everything works
a.slot = "dog"
a.matches?(String.new("dog"))
"s <=> @slot = 0"
=> true
What''s really odd is that called interactively, Case 1 works as
expected. When called from a script, it exhibits the oddity above.
Am I missing something fundamental about Ruby and string comparison?
- ff
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You''ll want to hit the ruby-talk list with this question.
On Feb 10, 2010 7:58 PM, "fearless_fool"
<rdpoor-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
This is more a Ruby than a Rails question -- feel free to redirect me
as appropriate -- but either this is a Ruby 1.9 bug or I have some
serious misunderstanding. Essentially, I''ve caught the <=>
operator
returning nil -- not -1, 0, or 1, but nil. Schematically:
class A
attr_accessor :slot
fun matches?(s)
p "s <=> @slot = #{s <=> @slot}"
return (s <=> @slot) == 0
end
end
Driven from a script, I get something like this:
# Case 1: Notice that <=> evaluates to nil when it should eval to 0
a.slot = "dog"
a.matches?("dog")
"s <=> @slot = "
=> false
# Case 2: When I pass a String.new("dog") everything works
a.slot = "dog"
a.matches?(String.new("dog"))
"s <=> @slot = 0"
=> true
What''s really odd is that called interactively, Case 1 works as
expected. When called from a script, it exhibits the oddity above.
Am I missing something fundamental about Ruby and string comparison?
- ff
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fearless_fool wrote:> This is more a Ruby than a Rails question -- feel free to redirect me > as appropriate -- but either this is a Ruby 1.9 bug or I have some > serious misunderstanding. Essentially, I''ve caught the <=> operator > returning nil -- not -1, 0, or 1, but nil. Schematically: > > class A > attr_accessor :slot > fun matches?(s) > p "s <=> @slot = #{s <=> @slot}" > return (s <=> @slot) == 0 > end > end > > Driven from a script, I get something like this: > > # Case 1: Notice that <=> evaluates to nil when it should eval to 0 > a.slot = "dog" > a.matches?("dog") > "s <=> @slot = " > => false > > # Case 2: When I pass a String.new("dog") everything works > a.slot = "dog" > a.matches?(String.new("dog")) > "s <=> @slot = 0" > => true > > What''s really odd is that called interactively, Case 1 works as > expected. When called from a script, it exhibits the oddity above. > > Am I missing something fundamental about Ruby and string comparison? > > - ffCan''t reproduce with what you''ve given. ruby-1.9.1-p376 > class A ruby-1.9.1-p376 ?> attr_accessor :slot ruby-1.9.1-p376 ?> def matches? s ruby-1.9.1-p376 ?> puts "s <=> @slot = #{s <=> @slot}" ruby-1.9.1-p376 ?> (s <=> @slot) == 0 ruby-1.9.1-p376 ?> end ruby-1.9.1-p376 ?> end => nil ruby-1.9.1-p376 > a = A.new => #<A:0x000000041915b8> ruby-1.9.1-p376 > a.slot = "dog" => "dog" ruby-1.9.1-p376 > a.matches? "dog" s <=> @slot = 0 => true ruby-1.9.1-p376 > String comparison via <=> to nil will return nil. Are you entirely sure that in your IRB session your object''s @slot isn''t nil for some reason? -- Posted via http://www.ruby-forum.com/. -- You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en.
On 11 February 2010 00:57, fearless_fool <rdpoor-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:> Essentially, I''ve caught the <=> operator > returning nil -- not -1, 0, or 1, but nil. Schematically:Do you need the <=> operator? (specifically, nothing you''re doing seems to care whether the compared string is bigger or smaller, only different. So why not use != instead? In fact, your matches? method could just as easily be: def matches?(s) s == @slot end which will return true if they''re equal, or nil if they''re not. If it has to be true/false, then use !!(s == @slot) -- You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk+unsubscribe@googlegroups.com. For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en.
> Can''t reproduce with what you''ve given. > > ruby-1.9.1-p376 > class A > ruby-1.9.1-p376 ?> attr_accessor :slot > ruby-1.9.1-p376 ?> def matches? s > ruby-1.9.1-p376 ?> puts "s <=> @slot = #{s <=> @slot}" > ruby-1.9.1-p376 ?> (s <=> @slot) == 0 > ruby-1.9.1-p376 ?> end > ruby-1.9.1-p376 ?> end > => nil > ruby-1.9.1-p376 > a = A.new > => #<A:0x000000041915b8> > ruby-1.9.1-p376 > a.slot = "dog" > => "dog" > ruby-1.9.1-p376 > a.matches? "dog" > s <=> @slot = 0 > => true > ruby-1.9.1-p376 > > > String comparison via <=> to nil will return nil. Are you entirely sure > that in your IRB session your object''s @slot isn''t nil for some reason?First, yep, 100% sure that @slot wasn''t nil -- I printed it out upon entering the matches? method. (FWIW, you have it reversed: irb session worked fine. Driven from a script failed.) Sadly, my attempts to prune down the example to a reproducible losing case have failed to fail, so to speak. As suggested by @Matt Brown, I''ll take this over to the ruby-talk list. Thanks. -- You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To post to this group, send email to rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org To unsubscribe from this group, send email to rubyonrails-talk+unsubscribe@googlegroups.com. For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en.